Nice editing, not too much though as IMO too much editing ruins the video and takes the concentration off what the player is actually doing.
A decent lengthed intro, anything longer than 45 seconds i find boring though.
Try to get good clips with guns which are seemed as 'less powerful', for example, m14, uzi, etc, guns which people don't use all the time.
Back to back long distance no scopes are always good in montages.
Sniper triples/ back to back collats,
Grenade quads or more
Dont include killstreak play, unless its like a quad rc xd or valkeryi.
Sync the music with the gameplay, but dont sync all the way through, try to make the best shots occur when the music drops etc.
this is all IMO...